1. Field of the Invention
The present invention generally relates to an image carrier toner unit and an image forming apparatus and more particularly to a replaceable image carrier toner unit and an image forming apparatus having the image carrier toner unit such as a copying machine, a printer, a facsimile machine, and the like.
2. Description of the Related Art
Patent Document 1 discloses what is called a process cartridge in which at least one of a development device as an imaging unit, a charging device, a cleaning device, and the like, are integrally formed and the process cartridge is detachable from an image forming apparatus.
Such a process cartridge has a merit in that a user is readily capable of replacing or maintaining the process cartridge without help of service-providing experts. In other words, in order to position the imaging unit around a photoconductor, the process cartridge is constructed such that the photoconductor, a container of a cleaning device rotatably supporting the photoconductor, and the development device are integrated, in which a charging roller for uniformly charging the photoconductor, a cleaning blade for scraping toner residual after a toner image is transferred to paper or an intermediate transfer body, and the like are attached to the cleaning container. Such a process cartridge is detachable from the image forming apparatus and can be replaced by the user when a life of the photoconductor is ended or waste toner is full.
However, in the structure where the photoconductor and the imaging device are integrally formed, there has been a problem conventionally pointed out in that even when a portion of the photoconductor or the imaging apparatus is to be replaced, the whole process cartridge must be replaced.
On the other hand, Patent Document 2 discloses a two-station recording system. In the two-station recording system, the development device, a writing device, and a driving unit are supported by an apparatus body via a common assembling member such that positions thereof are maintained in a high precision manner. Since the development device is positioned on the apparatus body based on such a structure, the development device is configured to be a positional base (base of assembly) in an entire imaging process element. The photoconductor (or photoconductor unit) is not the apparatus body but is embedded in the development device. In other words, the photoconductor (or photoconductor unit) is positioned on the development device based on a relationship where the development device is a main element and the photoconductor (or photoconductor unit) is a subordinate element. And, the photoconductor (or photoconductor unit) is detachably attached to the development device, so that the photoconductor (or photoconductor unit) is solely detachable. Further, the development device is also detachably attached to the image forming apparatus. In addition, in an embodiment, a photoconductor drum, a charging unit, and a cleaning unit are integrated.
In recent years, demands for image forming apparatuses such as printer, copying machines, and the like in the market have been increasingly complicated and sophisticated. In accordance with this, loading of the imaging device in image forming is increased. It has been understood that the demands in the market are further adding load to the imaging unit, particularly to the photoconductor. This is described from three factors in the following.
1. Miniaturization of Photoconductors Along with Miniaturization of Image Forming Apparatuses
In recent years, there have been demands for miniaturization of OA machines in the market. In accordance with this, imaging devices are required to be downsized. However, when photoconductors are downsized, namely, diameters thereof are reduced, consumption of the photoconductor per sheet is increased when an image is formed under the same conditions. For example, when the diameter of the photoconductor is reduced from 120 mm to 40 mm, the photoconductor must be rotated three times the photoconductor whose diameter is 120 mm so as to form an image of the same size. Accordingly, various types of consumption the photoconductor receives upon image forming, electric consumption from discharge at a charging unit, for example, and mechanical consumption from a blade at a cleaning unit become three times.
Conventionally, although development devices and the like have been miniaturized to some extent, photoconductors have not been miniaturized in comparison with other imaging devices in order to avoid the above-mentioned consumption, for example. However, with the increasing demands for miniaturization, it is impossible to avoid the miniaturization of photoconductors. In this manner, the demands for miniaturization increase load on photoconductors and reduce life thereof.
2. Thin Film Forming for Photoconductors Along with Achievement of High Image Quality
In recent years, users have increasingly output documents of photographic images and graphic documents. In accordance with this, high image quality has been developed for the purpose of achieving image quality of silver halide photography. However, upon realizing high resolution in electrophotography, the photoconductor is required to be a thin film. For example, in a case of a negatively-charged photoconductor, carriers formed by exposure in a CGL (Charge Carrier Generation Layer) pass through a CTL (Charge Carrier Transport Layer) and reach a surface of the photoconductor, thereby forming a latent image. If a thickness of the CTL is large, a length the carriers are moved is increased, so that the carriers come away from one another due to electric repulsion when the carriers are moved.
In such a case, a latent image is not formed as exactly as writing signals. As a result, an image in which dot positions are slightly displaced is formed. Such a problem is not limited to realization of high resolution in electrophotography from 600 dpi to 1200 dpi, for example. This problem is also generated upon improving image quality while the resolution is maintained to be 600 dpi so as to try to meet demands for high image quality in recent years.
In order to avoid such a case, it is necessary to make the photoconductor a thin film and reduce the movement length of carriers. Accordingly, photoconductors are made of thin films in recent years. However, the photoconductor experiences consumption due to scraping by a cleaning blade in each image forming, so that the life of the photoconductor is ended in a fewer number of image forming as the photoconductor film becomes thinner, thereby reducing the life of the photoconductor.
3. Increase of load on Photoconductor Along with Color Images
In recent years, color images have been increasingly output in the market due to readiness of comprehension of information and the like. Differing from monochrome images, in many cases, subjects to be output in color images include photographic images and graphic images occupying a wide area on paper for recording an image. Also, a solid color portion is in a background portion in many cases. In accordance with this, an imaging area upon per image forming is increased and consumption of the imaging device is increased along with the imaging area.
On the other hand, revolver type image forming apparatuses, for example, in which plural development units are employed for one photoconductor have been conventionally well known. Such image forming apparatuses are capable of forming color images at relatively a low cost as the number of parts is small. However, a latent image is developed in the photoconductor by the plural development units, so that the consumption of the photoconductor becomes several times greater than that of the development units. Thus, the consumption of the photoconductor along with color images is particularly large. Color images are one of factors in reducing the life of the photoconductor.
Patent Document 1: Japanese Laid-Open Patent Application No. 2000-075733
Patent Document 2: Japanese Laid-Open Patent Application No. 11-295952
Patent Document 3: Japanese Laid-Open Patent Application No. 2002-108171
As mentioned above, it is possible to readily estimate the life of the photoconductor relatively reduced in comparison with other imaging devices. Although researches on improvement of durability and life of photoconductors have been developed, researches on improvement of durability and life of other imaging devices have also been developed, so that the life of photoconductors tends to be relatively reduced.
This tendency causes imbalance of life in the photoconductor in the process cartridge and other imaging units. In other words, conventionally, it has been pointed out that the process cartridge has a problem in that an entire process cartridge must be replaced along with one of the imaging units with the shortest life. This problem becomes further obvious due to the reduced life of the photoconductor and a harmful effect may be caused, in which other imaging units are replaced along with the photoconductor with the shortest life.
In such a case, there are generated a financial burden for users resulting from disposition of imaging devices whose life is not ended, waste of labor of manufacturers collecting process cartridges, and negative effects on the environment. In particular, consideration for the environment is a worldwide concern and liability of manufacturers in the modern society, which must be given top priority. Process cartridges that have given priority in terms of usability must be given priority in terms of the environment.
In view of this, in order to prevent such harmful effects resulting from the demands of the recent market/society, Patent Document 3 discloses an image forming apparatus. In the image forming apparatus, it is possible to solely and preferentially replace a constituent element with a short life among plural constituent elements constituting the image forming apparatus. According to an embodiment in Patent Document 3, only a photoconductor is configured as a photoconductor cassette separately from a development unit and a cleaning unit. And, it is possible for a user to solely replace the photoconductor cassette. In addition, even in a case of plural photoconductors such as a tandem image forming apparatus, it is possible to replace each photoconductor at different replacement time. As mentioned above, Patent Document 3, in which it is possible for a user to replace each photoconductor, gives top priority to the environment and also reduces burden for users and manufacturers, so that problems regarding process cartridges are eliminated. Preferably, trouble for users is eliminated by improving usability. Further, operations the users must perform more frequently than the replacement of the photoconductor include replacement and supply of toner which is consumed greater than the photoconductor and the replacement and supply of toner lays a burden for the users. However, the users consider the replacement and supply of toner to be the same as replacement of ink of a ball-point pen or supply of staples to a stapler. Thus, although the replacement and supply of toner is troublesome, this has been taken for granted by the users. However, in addition to the replacement and supply of toner which has not been regarded as greatly bothersome, if the replacement of the photoconductor with a high replacement frequency following the toner having different replacement and supply time is added, it is naturally expected that the users are significantly dissatisfied with such inconvenience and trouble.